How population combobox with dependency of code product.

Select * from Produto where code_product = textbox_code_product

I tried to use the code below

private void prj_cod_Leave(object sender, EventArgs e)
{
sysProjetoEquipamentoBO1.FillDataTable("SELECT * FROM tabproj_equipamento WHERE prj_nrow = " + sysProjetoBO1.prj_nrow);
}

but he did not give certain. I have a field sysProjetoBO1.prj_cod and sysProjetoBO1.prj_nrow in the same table. I need to show prj_cod and populate combobox for the code sysProjetoBO1.prj_nrow. Combobox populated is sysProjetoEquipamentoBO1.prj_nrow!

Well I am not totally certain what you are trying to do.  But let's back up and start here.  First, all SF lists allow you to populate via a BO.  You will not want to just slap in SELECT code.  You will want to create a Fill command that accepts whatever parms that you need for population.

Second, you will want to set the combo being populated to populate Manual instead of FormLoad because you are going to want to first ensure that your dependent code is set.

Third, once you have created a Fill method and setup the PopulationDataSourceSettings to use that fill method on the Combo, then you will want to handle the ListPopulating event to provide the value from the dependent code.

Finally, there are a TON of samples on this.  This is an extremely common task done within the framework.  There are samples that come with the framework showing how to do this, you can look at the StrataFlix sample, or just search on the ListPopulating event within the forum and you will find a LOT of samples.